A computer readable disk has thin layers of magnetic material coated on its surfaces. Storage data are laid down along circular tracks around the disk surface. To enable a read-write head to know where it is positioned, servo data is pre-recorded along circular tracks on the disk. These servo data contains information being read by the head and subsequently being interpreted by the servo system firmware to determine which track the head is on. For one offline media servo-writing scheme, the servo data pre-recording process is carried out before the disks are placed inside a hard drive. The disks are servo-written on a dedicated equipment (media servowriter) inside the clean room. One advantage of this scheme is that multiple disks (usually 5 to 25 disks) can be servo-written at one time using the same set of hardware. As hard drives nowadays usually only contain one to two disks, in-drive servo-writing (disk media installed in the disk drive before servo writing) can take up a lot of clean room space and time. By servo-writing multiple disks outside the drive, usage of clean room space and time can be substantially reduced. Using higher performance components such as high precision air bearing spindle and high resolution positioner, a dedicated equipment for servo-writing is capable of writing servo-tracks with higher quality. This becomes especially important as the track density of the disk media increases.
For consumer electronic applications, small form factor disk drives are most popular for MP3 player, hand held digital organizer or cell phone and GPS devices and so on. A uni-mount style head is needed for media servo writing on these types of disk media. The characteristic of this kind of head is the pivot arm which is made of stainless sheet metal and welded with head suspension to become one integrated component; hence the traditional E-block to mount heads is not required. One of the prior arts (U.S. Pat. No. 6,055,133 by Albrecht) shows the unamount style head suspension assemblies that stack multiple spacers and heads together.
FIG. 1 shows an exploded view of a unamount head/arm subassembly with two read-write heads known to those skilled in the art. The unamount head/arm subassembly is typically assembled by mounting two head/arm units 2 and an actuator arm 3 on an assembly bearing 4 and locking the assembly with a square nut 1, wherein the actuator arm is interposing between the two head/arm units. The head alignment is accomplished by inserting a pin 6 into the two tooling holes 5 of both head/arm units. FIG. 2 shows a perspective view of the assembled unamount head/arm subassembly as shown in FIG. 1. The alignment capability is +/−0.002″ for two heads.
FIG. 3 shows a partially exploded view of a unamount head stack assembly comprising a plurality of unamount head/arm subassembly. As afore-mentioned, each unamount head/arm subassembly comprises two head/arm units 2 that are interposed with a spacer 7. The plurality of unamount head/arm subassemblies are mounted onto an assembly bearing 8, and locked with a collar 9a and a nut 9b. FIG. 4 shows a perspective view of the assembled unamount head stack assembly as shown in FIG. 3. Again, the head alignment is accomplished by inserting a pin 10 into the tooling holes through about 10 to 50 head/arm units. The alignment capability is +/−0.005″ at best. When one or more read-write heads are not working properly, the whole assembly has to be dismantled in order to rework on the malfunction heads. The extra handling will damage the sensitive head/arm subassemblies.
In practice, epoxy is used to prevent looseness before assembly is tightened together with a nut. It might be all right for disk drive with one or two heads. In this case, whenever the head rework is needed, just disassemble the whole head stack or scrap the whole assembly. For a media servo writer, 5 to 25 media disks are written at the same time, and the head stack assembly includes 10 to 50 heads (each disk surface needs one head). It is not practical to disassemble whole arm/actuator in order to rework one or two defective heads.
Furthermore, it is especially crucial for small form factor drive that outside track should start as close to the disk outer diameter as possible so that the predictable number of tracks can be written and disk drive capacity can be guaranteed. In addition, the heads need to be aligned as close as possible in order to make sure that all heads will start from the same most inward or outward positions of the disks to produce the highest number of data tracks.